Study On Selective C-H Activation Of Quinoline N-Oxide

Quinoline derivatives are one of the most valuable compounds and have been found widespread application in diverse areas,such as bioactive natural products,pharmaceuticals and functional materials.Therefore,research on efficient synthetic methods to synthesis various functionalized quinoline derivatives is an important subject for organic chemists.This article focuses on the transition metal catalyzed or visible light-induced C-H activation reaction of quinoline N-oxides.The main contents are as follows:（1）We have developed a convenient carbo-acylation reaction of quinoline N-oxides with a-diketones via palladium catalyzed C-H and C-C bond activation in the presence of TBHP.The reaction system mainly undergoes three processes of cyclopalladiumation,oxidative addition and reduction elimination,and also involves a free radical process.Various quinoline N-oxides and a-diketones derivatives were well tolerated in this catalytic system,which adds a new synthetic method for the functionalization reaction of quinoline-N-oxides,yield has 70%-80%.（2）C2 carbamoylation of quinoline N-oxides with 4-phenylsemicarbazide derivatives was achieved under Cu Br catalyzed.The reaction selected 4-phenylsemicarbazide as the carbamoyl source,which further extended the quinoline N-oxides C2 functionalization.When the reaction was conducted in the presence of butylated hydroxytoluene（BHT）and 2,2,6,6-tetramethylpiperidine-1-oxyl（TEMPO）as a radical trapping reagent,the reaction was seriously suppressed.These results indicated that a free radical intermediate was involved in this reaction.The reaction is easy to operate,has good selectivity and high tolerated,yield has63%-90%.（3）Copper-catalyzed C2-Sulfonylation of quinoline N-oxides with DABSO and phenyldiazonium tetrafluoroborates for the synthesis of C2-sulfonylquinolines via a radical reaction under N₂ protected.The reaction used DABSO as the sulfonyl source,which is safer and less toxic than traditional sulfonylation reagents.In addition,the phenyldiazonium tetrafluoroborates also has higher reactivity,and has good tolerated to electron donating or electron withdrawing groups,yield has 60%-86%.Mechanism studies indicated that free-radical intermediates are involved in the reaction.（4）A simple and efficient method for the synthesis of 2-sulfonylquinoline from deoxygenativeC2-sulfonylation of quinoline N-oxides with sulfinic acid induced by visible light is presented.In the reaction,Na₂-Eosin Y was used as photocatalyst,and sulfinic acid as sulfonylation reagents.Various functional groups were well tolerated in this reaction and the corresponding products were obtained with a yield of 72%-96%.The reaction is induced by visible light,conforms to the concept of green chemistry,and has high environmental friendliness.Furthermore,the method further enriches the types of sulfonylated substrates.